The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Perpendicular magnetic recording, in which the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer of a magnetic medium, allows for ultra-high recording densities in magnetic recording systems, such as HDDs. The write head must be able to write data not only at high bit-density but also at high data-rates. However, the switching time for the write pole of the write head to switch from one magnetization direction to the other is a limiting factor to the speed of magnetic switching as the data rate is increased. At high data-rates, the available magnetic flux from the write head, as seen by the recording layer on the magnetic medium, is limited by the low-frequency flux output of the write head.
It is also known that additional overshoot of the write current from the HDD's write driver circuitry may aid in the magnetization reversal speed. Write enhancement circuitry that provides additional overshoot beyond that provided by the write driver circuitry aids in overcoming signal transmission losses and reduces the required overshoot from the write driver.
To provide such overshoot, a single capacitor design has been proposed. FIG. 1 shows a wafer view 50 and a side view 80 of such a design, according to the prior art, Passive transmission line compensation is provided with a capacitor 52 that has been added between two layers of electrically-conductive material 54, 56 that serve as the capacitor plates. However, this design using a single capacitor 52 may cause a large impedance misbalance between the coil leads 58, 60 and the substrate 64, shown as a single parasitic capacitance 62. This parasitic capacitance 62 is undesirable but also unavoidable due to the thinness of wafer materials in the write head. When the capacitance is imbalanced at the write head, common-mode disturbances (spikes) and crosstalk problems may result. Common-mode voltage/current may occur during write signal transitions, while write-to-read crosstalk is caused by common-mode signals. The signal disturbances are harmful to the sensitive read element, and may damage the read element if not neutralized.